\section{Use-case: Choose seats} 
\paragraph*{Actor: User}
\paragraph*{Frequency:}
Peak load: 0-200 an hour, needs to be scalable.
\paragraph*{Preconditions:}
User exists and is logged in. \\
Travel route network is existent. \\
The user has already reserved and booked tickets. \\
Optional: The user is physically present at the airport electronic checkin terminal.
\paragraph*{Postconditions:}
Specific seats within the plane has been reserved, the number of seats depends on how many passengers the user has booked tickets for.

\paragraph*{Primary flow:}
\begin{enumerate}
\item The system shows possible seats within the plane.
\item The user chooses seat(s) from seats which are not already chosen.
\item The selected seats are locked for 2 minutes.
\item The user clicks "Reserve seats" and the seats are locked for an additional 1 minute.
\item The user is shown a message box asking to confirm the chosen seats.
\item The user clicks "Confirm".
\item The system reserves and locks the selected seats indefinitely.
\end{enumerate}

\paragraph*{Alternative flow:}
4a. The selected seats are unlocked and available to other users after 2 minutes. \\ \\
6a. The selected seats are unlocked and available to other users after an additional minute and the message box is closed. \\ \\
6b. The user clicks "No, choose different seats"; the message box is closed, the selected seats unlocked and available to other users.